The acid-catalysed cleavage of 1,4-dimethyl-1,4-dihydronaphthalene-1,4-endoperoxide gives the 4-hydroxy, methoxy, trifluoroacetoxy, formyloxy, bromo, and chloro methyl derivatives of 1-methylnaphthalene in yields of 36,38,52,76,77, and 100% respectively when water, methanol, trifluoracetic, formic, hydrobromic, or hydrochloric acids are used as reagents.